The big advantage of email is its federation and no need for end-to-end connectivity (Store and Forward paradigm). Today due to cloud computing this could be at

The big advantage of email is its federation and no need for end-to-end connectivity (Store and Forward paradigm). Today due to cloud computing this could be attempted as a monolithic service and the messages can be stored in the cloud until delivery (or even afterwards). So a new email protocol should take into account if it needs federation (distributed) or not and what would be the intended reach.